Also known as the Battle Sage, Rahan is a powerful, very old, practitioner of the Slayer Fist style of martial arts. He was the master and surrogate father of the saran Kurai, who would later become one of the Holy Ghost's 4 Warlords, and would later accept the Dark Prince Cain as a disciple as he had been Kurai's pupil. For thousands of years he wandered the Galaxy to test his fighting skills, but after Kurai left him, he retired to the planet Vellum, where he had once killed 4000 Monks who had offended him.

Unbeknownst to most throughout the Galaxy is that Rahan is actually a Watcher. In the time of the Age of the Gods, he was birthed from the same genetic stock as the rest of his people and given high rank within the Holy Order. However, Rahan came out different from his brothers, possessing a violent disposition and disagreeable attitude. The name Rahan is actually the Watcher word for "weird" or "different" (Watchers do not generally take names). Impressed with the pluck and uniqueness of this aberrant Watcher, the God Shine took him under his wing and taught him martial arts. Rahan was among the Watchers who stood with Shine against Shiva, and he survived that battle to be among those who created the All Union and SENTINEL.

Afterwards he left his people. It is unknown whether he was exiled or left of his own volition, as both he and the other Watchers seem to imply both at once. Upon leaving Rya, Rahan travelled the Galaxy, testing his skills, developing his martial arts, and acting as a sort of knight-errant erradicating villains with his own hands. However, he was also known for his violent temper, and it was not uncommon for him to obliterate anyone who offended him.

Rahan is visibly very different from other Watchers. Despite having the green skin, white hair and pointed ears common to his race, his face is weathered and wrinkled giving him the appearance of advanced age, unlike other Watchers who tend to look like children. However it should be noted that this appearance seems to be intentional on Rahan's part, and it is implied he can look as young or old as he wants. In flashbacks he wore the robes of the Holy Order, and after the Cataclysm he wore black robes emblazoned with the Crest of Shine. Currently he wears black pants, a long black jacket which falls to his knees, a white scarf, and metal bracers on his forearms and shins. He also commonly wears a conical hot and has since the days of the Gods worn his hair shaggy pulled back into a long ponytail. Though small, underneath his robes Rahan is heavily muscled with a powerful frame.

Rahan is the creator of the martial art known as Slayer Fist. Foregoing the pacifism bred into his people, Rahan created a style marked by incredibly powerful techniques for the sole purpose of destroying opponents. More than one person who's observed Slayer Fist in action describes it as "Pure Carnage." Rahan developed the style with the idea that a smaller and weaker person could kill a more powerful opponent, and the techniques are meant to apply the most power to the weakest areas of an enemy and kill them in as few blows as possible. The art's power lies into channeling one's energy in a single blow and striking into the Hidden Channeling Points through which Aura is emitted from the body. This causes the victim to explode, be controlled involuntarily or otherwise incapacitated. According to Cain, who inherited the style from Rahan's pupil Kurai, one of the key features of the style is that each blow injects an "Aura Bomb" into the body of the opponent which is meant to destroy them from the inside out.